A zoologist consulted by Essex police over reports of a lion in the Clacton area has said she thought the animal was "more likely to be a dog".

Sarah Forsyth, a rhino curator who lives on site at Colchester Zoo and was called to help the police investigate reports of a lion sighting, told the Guardian that pictures of the 'animal' were ambiguous and of poor quality.

Reports from frightened holidaymakers on Sunday triggered a police helicopter search and, nearly 24 hours later, the sighting continues to be taken seriously.

Forsyth and zoological director Anthony Tropeano of Colchester zoo arrived in St Osyth, where the sighting occurred, with tranquiliser equipment at the request of police, she said.

"By the time we got there whatever it was had gone. We were shown some photographs, but they were from very far away, very poor quality and to be honest there was no way of saying 'yes' or 'no'," Forsyth said.

Asked if she was sceptical that the animal pictured was a lion, she said: "I think it's unlikely. I think it was more likely to be a dog. It certainly wasn't a male lion. It didn't have a mane."

Forsyth, who police are keeping on standby for any further sightings, said they found no droppings or footprints to indicate the presence of a big cat. Asked whether she thought the police operation had been necessary, she said: "I think they kind of have to because there was no way of saying that it definitely wasn't a lion."

The police leading the search said on Monday they were taking the hunt seriously. Initially they warned residents to stay inside as officers began a search for the unusual target. But they later said residents could go outside.

A spokesman said: "Public safety is our priority, which is why we are taking the sighting and all associated evidence seriously. We have an increased police presence in the area which will offer reassurance to local residents, motorists and holidaymakers.

"We would encourage people to enjoy the bank holiday Monday, indulging in activities as they want to. For those who wish to take a walk in the countryside surrounding Clacton, then we would just ask them to be extra vigilant and cautious. However, they will probably see us first before they see anything else."